Within each group of observers, are some especially credible or especially not so?You (or your family or your class) are trying to decide whether you should buy a Mac computer or a Windows PC. You might consulta friend who owns either a Mac or a Windows machine. especially crediblea friend who now owns one of the machines but used to own the other. especially crediblea dealer for either Mac or Windows computers. especially not soa computer column in a big-city newspaper. especially not soreviews